alert("导入js文件");
var i;
alert(i);
i=300;
alert(i);
alert(typeof(i));
i="abc";
alert(i);
alert(typeof(i));

var a=12,b="abc";
alert(a*b);
alert(typeof(a*b));

a=123,b="123";
alert(a==b);
alert(a===b);